Broadband networks are systems of network components which receive and/or transmit broadband signals where the signals are analog wave forms within the 5 MHz (megahertz) to 1 GHz (gigahertz) frequency range; contain information encoded with analog modulation; and are combined through multiplexing (typically, frequency division multiplexing). These network components are interconnected through network connections. Examples of broadband networks include CATV/MATV (Community Access Television, Multiple Access Television) systems and data networks. A CATV/MATV system is typically composed of one or more "head-ends" which deliver television channels to a community of homes over an HFC (hybrid-fiber coax) infrastructure. The network components in a CATV/MATV broadband network include RF (radio-frequency) modulators, RF demodulators, frequency translators, band-pass filters, band-trap filters, combiners, splitters, taps, attenuators, equalizers, amplifiers, broadband switches, fiber-optic nodes, and metering equipment. These components are connected to each other through transmission lines, typically coaxial cable.
The CATV/MATV systems are said to be broadband networks because the information which flows between the CATV/MATV network components is encoded in analog signals within the 5 MHz to 1 GHz range. The RF modulator components receive analog or digital signals containing information (such as audio and video information or digital data) in the baseband spectrum (below 5 MHz) and modulate the signals into the broadband spectrum. Each individual RF modulator will typically restrict the modulation of its input signals to within a six megahertz band, or television channel; of the broadband spectrum. Television channel 2, for instance, is the band of broadband spectrum between 54 MHz and 60 MHz. A television channel 2 modulator will modulate its audio and video into this range so that a connected television receiver (demodulator) can receive it. Demodulators listen to network connections for modulated signals within the broadband spectrum and convert the modulated signal into one or more demodulated output signals. The frequency range which the demodulators listen to is typically coordinated with the frequency range that one or more modulators are broadcasting on so that a demodulator tuned to the spectrum range of 54 MHz to 60 MHz (channel 2), for instance, will demodulate and output the signals (such as audio and video or data signals) which were modulated by a connected channel 2 modulator. A fiber-optic node is another network component which generates and receives broadband information. These nodes up-convert signals on a given range of the broadband spectra (such as 5 MHz to 50 MHz) into the optical frequency spectrum for transmission over optical media such as fiber-optic cable. The nodes can also receive signals on a given range in the optical frequency spectrum and down-convert the signals into the broadband spectrum for transmission over a broadband network. Fiber-optic nodes are often used to interconnect with optical fiber, two or more broadband networks which are separated over long distances.
Many of the network components are directional in nature, that is, they receive broadband signals, perform a function over the broadband spectrum, and retransmit the altered signals. Frequency translators translate the signals in a given range of the broadband spectrum into a second range of the broadband spectrum. Amplifiers are used to rejuvenate signals which have decayed due to transmission losses. Band-pass filters attenuate signals (typically noise) in a given range of the broadband spectrum and attenuators attenuate signals over the entire broadband spectrum. Equalizers compensate for frequency dependent decay of signals over long distances of transmission lines (network connections).
Metering devices are network components which monitor and measure broadband signals. Examples of metering devices include spectrum analyzers and signal level meters.
RF switches are network components which selectively switch on or off the electric connectivity of network connections. An A/B RF switch, for example, has one common (input) network connector and two branch (output) connectors and can connect the common connector to either of the branch connectors. RF switches are available in different configurations with varying numbers of common (input) and branch (outputs) connectors. The AB-4, stock no. 4017, made by Blonder Tongue Laboratories, Inc. is a manual RF switch which has one common connector, two branch connectors, and is controlled through a push-button. Pushing the button, toggles the common connector between being connected to the first branch connector and the second. The VSESC-1 "Basic Coax Switch" made by Viewsonics, Inc. is an A/B RF switch which is controlled by applying DC voltage to a control line. When +12 VDC is present on the control line, the switch connects its common connector to one of its branch connectors. In the absence of the voltage, the switch connects its common connector to the other branch. Further, the "ClearPath Test Point Selector" (TPS) made by Electroline Systems, Inc. is an RF switch with eight branch connectors and one common connector. The TPS operates on the return bandwidth (5-40 MHz) of the broadband spectrum and can switch any one of the branches to its common. In contrast to the AB-4, the TPS is an addressable switch; it can be controlled remotely through an FSK (Frequency Shift Keying) modulated signal in the broadband spectrum. Currently, RF switches are employed at the periphery of the network to provide controllable connections to subscribers (turn service to a subscriber on or off); at strategic points in a cable plant to isolate and/or attenuate signals going to/coming from specific neighborhoods; and in the head-end of the cable plant to selectively switch metering devices into the broadband network. See http://www.electrolinequip.com on the World-Wide-Web, or the Electroline ClearPath product literature for more details. RF switches are usually constructed of discrete components including limited lifetime relays.